The viscosity of the pressurized actuating fluid used to hydraulically actuate an intensifier piston/plunger combination in a hydraulically-actuated unit fuel injector varies with the temperature of the actuating fluid. The magnitude of pressure drops in the actuating fluid circuit vary in accordance with the actuating fluid viscosity, thus affecting the amount of fuel delivered to the engine and the timing of the injection event relative to a predetermined engine crankshaft angle. The viscosity of the actuating fluid is highest under cold engine starting conditions, which results in fuel injection quantity and fuel injection pressure being greatly reduced and the timing of the fuel injection being retarded. Under these extreme conditions, engine starting is difficult.
One approach for solving these problems is to measure the ambient temperature of the fluid, determine a typical viscosity from the measured temperature, and make corrections to delivery, timing and pressure parameters to compensate for the increased viscosity. A problem arises, however, when engine lubrication oil is used as the actuating fluid. In such a system, the user generally controls the type and grade of oil and thus, even for a particular temperature, the viscosity of the engine lubrication oil/actuating fluid varies greatly. Since a temperature measurement alone is inadequate to measure viscosity, fuel injection quantity, timing and pressure parameters are incorrectly determined to compensate for the variation in the viscosity of the actuating fluid, which leads to less than optimal performance of the engine system.
The present invention is directed to overcoming one or more of the problems as set forth above.